1. Field of the Invention
This invention relates to a communication control program and method for controlling communication between computers and, more particularly, to a communication control program and method for performing communication via some transmission routes.
2. Description of the Related Art
In a LAN (Local Area network) or the like connecting computers, there is only one transmission route between the computers. If a trouble happens in a transmission route connecting computers, communication between the computers is interrupted. Therefore, for high reliable communication, extra communication equipment should be prepared.
For example, two LAN adaptors are installed in a system. One LAN adaptor is used as an operational host and the other is used as a standby host. When the operational host breaks down, the operational host LAN adaptor is made invalid while the standby host LAN adaptor is made valid instead (for example, refer to Japanese Unexamined Patent Publication No. 9-326810). With this technique, even if a trouble happens in one LAN adaptor, the other LAN adaptor can continue the communication.
As another technique, when a communication adaptor is switched to another in a system having some communication adaptors, the other communication adaptor performs multi-address transmission to send an ARP (Address Resolution Protocol) request message (for example, refer to Japanese Unexamined Patent Publication No. 10-320327). When a trouble happens, the communication adaptor can obtain the MAC (Media Access Control) addresses of other devices to establish the communication.
By the way, in many existing networks, when packet transmission is failed, this transmission is repeated until it is done successfully. When the packet transmission is failed a prescribed number of times, a process such as an application recognizes that the connection has been disconnected, and establishes another connection via a different transmission route.
However, a conventional method of switching connections takes time from occurrence of a transmission route trouble until when a process such as an application recognizes disconnection of the connection. This is because the transmission route trouble is not detected until the packet transmission is failed several times. Therefore, communication between processes of different computers is suspended while the packet transmission is repeated. This deteriorates processing efficiency of the network.
Further, even if there are some physically different transmission routes between computers, only part of the routes are different. In the patent references 1 and 2, only LAN adaptors (communication adaptors) are different. Alternatively, some different transmission routes via the same router may be prepared to select an efficient route. However, these cases where only part of the transmission routes is different may be insufficient in reliability for some system uses. In addition, route selection by specifying a device such as a router deprives a degree of freedom in which some routes are simultaneously used.